Pen fault detection

Abstract

There is provided an electronic device for detecting a Protective Earth and Neutral (PEN) fault in a three phase L1, L2, L3 power supply. The electronic device 700 being configured to determine a refe

Description

Technical Field The disclosure herein relates to detecting PEN faults, for example in an electrical vehicle charging system. More specifically, the disclosure herein relates to detecting protective earth and neutral faults in a three phase power system. Background Electric vehicles (EVs) are becoming increasingly popular as a more environmentally friendly mode of transportation. However, to support the expanding fleet of EVs, there is a growing need for an efficient and safe EV charging infrastructure. In the UK, many EV chargers are supplied electrical power from a Protective Earth and Neutral (PEN) distribution network. Unfortunately, a PEN fault can create a hazardous situation where touching an EV that is being charged could give the user an electric shock. To ensure safety, all EV chargers in the UK must be equipped with a system to detect PEN faults. This is particularly challenging for 3-phase chargers, which usually require additional hardware to detect the fault. These added components increase the cost and size of the charger. Various methods for detecting PEN faults have been developed, such as directly measuring the live voltage relative to an earth reference voltage in order to detect a fault voltage or using current transformers to measure the live current to detect a fault current. However, these methods have implementation restrictions, especially for domestic households where a reliable and well-grounded earth reference point is not usually present. As a result, implementing these methods could lead to additional complications and cost to the EV charging system and / or its installation. Summary According to a first aspect of the present disclosure, there is provided an electronic device for detecting a Protective Earth and Neutral (PEN) fault in a three phase power supply. The electronic device being configured to determine a reference voltage. The reference voltage is derived from a first voltage, a second voltage and a third voltage each associated with a respective phase of the three phase power supply. The first voltage is measured between a first phase conductor of the three phase power supply and a reference conductor associated with the three phase power supply. The second voltage is measured between a second phase conductor of the three phase power supply and the reference conductor. The third voltage is measured between a third phase conductor of the three phase power supply and the reference conductor. The electronic device is further configured to detect a PEN fault based on a comparison of the reference voltage with a threshold voltage. Optionally, the reference conductor is a neutral conductor associated with the three phase power supply or a protective earth conductor associated with the three phase power supply. Optionally, determining the reference voltage comprises determining an average of the first voltage, the second voltage and the third voltage. Optionally, the comparison of the reference voltage with the threshold voltage comprises deriving a root mean square, rms, reference voltage from the reference voltage. Optionally, detecting the PEN fault comprises determining that the rms reference voltage exceeds the threshold voltage. Optionally, the threshold voltage is 70 volts rms. Optionally, the electronic device is further configured to detect an interruption to at least one phase conductor of the three phase power supply based on a comparison against a second threshold of at least one of the following: the first voltage; the second voltage; the third voltage; a voltage difference between the first phase conductor and the second phase conductor; a voltage difference between the second phase conductor and the third phase conductor; and / or a voltage difference between the third phase conductor and the first phase conductor. Optionally, the comparison of at least one of the first voltage, the second voltage, the third voltage, the voltage difference between the first phase conductor and the second phase conductor, the voltage difference between the second phase conductor and the third phase conductor and / or the voltage difference between the third phase conductor and the first phase conductor with the second threshold comprises: deriving at least one of a root mean square, rms, first voltage from the first voltage, an rms second voltage from the second voltage, an rms third voltage from the third voltage, an rms fourth voltage from the voltage difference between the first phase conductor and the second phase conductor, an rms fifth voltage from the voltage difference between the second phase conductor and the third phase conductor and / or an rms sixth voltage from the voltage difference between the third phase conductor and the first phase conductor; and comparing the derived rms first voltage, rms second voltage, rms third voltage, rms fourth voltage, rms fifth voltage and / or rms sixth voltage with the second threshold. Optionally, detecting the interruption to the at least one phase conductor of the three phase power supply comprises determining that the rms first voltage, the rms second voltage, the rms third voltage, the rms fourth voltage, the rms fifth voltage and / or the rms sixth voltage is less than the second threshold voltage. Optionally, wherein the second threshold voltage is derived from the nominal voltage of the three phase power supply. Optionally, wherein the electronic device is further configured to measure the first voltage, the second voltage and the third voltage. Optionally, wherein the electronic device is further configured to, upon detection of the PEN fault, generate a flag indicative of the detection of the PEN fault. Optionally, wherein the electronic device is further configured to, upon detection of the PEN fault, trigger an alarm. Optionally, wherein the electronic device is further configured to, upon detection of the PEN fault, disable the three phase power supply to the EV charger. According to a second aspect of the present disclosure, there is provided a system for use in an Electric Vehicle (EV) charger. The system comprising: the electronic device of any preceding statement; and a metrology measurement unit. The metrology measurement unit being configured to measure the first voltage, the second voltage and the third voltage; and output, to the electronic device, measurements of the first voltage, second voltage and third voltage. According to a third aspect of the present disclosure, there is provided an Electrical Vehicle (EV) charger comprising the system of the previous statement. According to a fourth aspect of the present disclosure, there is provided a method for detecting a Protective Earth and Neutral (PEN) fault in a three phase power supply. The method comprising determining a reference voltage. There reference voltage is derived from a first voltage, a second voltage and a third voltage each associated with a respective phase of the three phase power supply. The first voltage is measured between a first phase conductor of the three phase power supply and a reference conductor associated with the three phase power supply. The second voltage is measured between a second phase conductor of the three phase power supply and the reference conductor. The third voltage is measured between a third phase conductor of the three phase power supply and the reference conductor. The method further comprising to detecting a PEN fault based on a comparison of the reference voltage with a threshold voltage. Optionally, the reference conductor is a neutral conductor associated with the three phase power supply or a protective earth conductor associated with the three phase power supply. Optionally, determining the reference voltage comprises determining an average of the first voltage, the second voltage and the third voltage. Optionally, the comparison of the reference voltage with the threshold voltage further comprises deriving a root mean square, rms, reference voltage from the reference voltage. Optionally, detecting the PEN fault comprises determining that the rms reference voltage exceeds the threshold voltage. Optionally, the threshold voltage is 70 volts rms. Optionally, detecting an interruption to at least one phase conductor of the three phase power supply based on a comparison against a second threshold of at least one of the following: the first voltage; the second voltage; the third voltage; a voltage difference between the first phase conductor and the second phase conductor; a voltage difference between the second phase conductor and the third phase conductor; and / or a voltage difference between the third phase conductor and the first phase conductor. According to a fifth aspect of the present disclosure, there is provided a computer program comprising instructions which, when executed by at least one processor, perform the steps of any preceding method statement. According to a sixth aspect of the present disclosure, there is provided a computer readable medium comprising the computer program of the previous statement. Brief Description of the Drawings The invention shall now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates a schematic diagram of a power supply system for charging an Electric Vehicle (EV). Figure 2 illustrates a schematic diagram of the power supply system of Figure 1 for charging an Electric Vehicle (EV) with an open circuit fault. Figure 3 is a circuit diagram representing a three phase supply. Figure 4 illustrates the three-phase voltages across resistors RI, R2, and R3 in the circuit of Figure 3. Figure 5 illustrates a circuit diagram 500 that shows an example of an open circuit fault. Figure 6 illustrates the three-phase voltages across resistors RI, R2, and R3 in the circuit of Figure 5. Figure 7 is a block diagram showing a system 700 for detecting PEN faults according to an example implementation. Figure 8 is a block diagram showing a system 800 for detecting PEN faults according to another example implementation. Figure 9 is a block diagram showing a system 900 for detecting PEN faults according to another example implementation. Figure 10 is a block diagram showing a system 1000 for detecting PEN faults according to another example implementation. Detailed Description A PEN fault is a type of fault that can occur in electrical installations where the protective earth conductor (PE) and the neutral conductor (N) are interconnected. A PEN fault can occur when the PEN conductor becomes disconnected from the supply, which can happen due to various reasons, such as mechanical damage to cables, or aging or degradation of insulation materials. Many EV chargers are supplied electrical power from a PEN distribution network. In the context of EV chargers, PEN faults can be extremely dangerous because when a person comes into contact with the EV, electricity can flow through the person's body and cause an electric shock to the person. Therefore, EV chargers are often required to have a mechanism in place to detect such faults and prevent any accidents or injuries from occurring as a result of a PEN fault. In the UK, the IET (Institution of Engineering and Technology) Wiring Regulations BS 7671:2018 stipulates various different requirements and techniques for providing protection, which includes a stipulation that "Protection against electric shock is provided by a device which electrically disconnects the vehicle from the live conductors of the supply and from protective earth in accordance with Regulation 543.3.3.101(ii) within 5 s in the event of the voltage between the circuit protective conductor and Earth exceeding 70 V rms due to an open-circuit fault in the PEN conductor of the low voltage network". This regulation sets out the requirement that mechanisms that are used to detect PEN faults in EV chargers must ensure that disconnection of the EV charger from the supply when the voltage between the circuit protective conductor (the neutral conductor) and Earth exceeds 70 V rms. The present disclosure provides a novel solution to detect PEN faults in an EV charger and ensures compliance with UK regulations related to EV chargers. The disclosure herein involves the use of an electronic device for detecting a PEN fault in an EV charger supplied from a three phase power supply. The electronic device disclosed herein derives a reference voltage based on measured voltages between the three phase conductors of the three phase power supply and a reference conductor associated with the three phase power supply. The electronic device disclosed herein is further configured to detect a PEN fault based on a comparison of the reference voltage with a threshold voltage The invention provides an effective solution to detect PEN faults in EV chargers, enabling the prevention of electric shocks to any person touching the EV or EV charger. Furthermore, the electronic device disclosed herein provides basis for complying with UK regulations related to EV chargers. Moreover, the disclosure provided herein makes use of measurements that may already be made as part of metrology measurements in an EV charger, in which case additional, dedicated PEN fault detection hardware, or complex installation procedures, may be unnecessary. This may result in the PEN fault detector disclosed herein being both cost-effective and straightforward to implement. As such, the disclosed PEN fault detection functions disclosed wherein may be easily integrated into existing EV charging devices without significant modifications or disruptions to the system. This means that existing EV charging stations may be retrofitted with the disclosed PEN fault detection apparatus, or new EV chargers can straightforwardly and inexpensively be designed with the disclosed PEN fault detection functionality integrated, resulting in safer and more reliable charging systems for EVs. Figure 1 illustrates a schematic diagram of an example power supply system 100 for charging an Electric Vehicle (EV). The power supply system 100 is divided into two sections: the supply side and the customer side. The supply side comprises a transformer 110 that is connected to a live, or phase, conductor line 120 and a PEN conductor 130 that supplies both neutral and protective earth (PE) to a customer premise. Whilst only a single live / phase conductor line 120 is represented in Figure 1 for the sake of simplicity, for a three phase power supply there will in fact be three live / phase conductor line 120 - one for each supplied phase voltage. On the customer side the PEN conductor is split into a Neutral Conductor 180 and a Protective Earth Conductor 170.An EV body / chassis 150 is shown, which includes an EV onboard-charger load 160 that represents the charging load of an EV. Again, whilst only a single load 160 is represented in Figure 1 for the sake of simplicity, for a three phase power supply there will in fact be three loads 160 - one for each supplied phase voltage. The EV load 160 is connected to the transformer 110 via the phase or live line 120, and the PEN line 130 The EV body / chassis is connected the Protective Earth Conductor 170 in most configurations. Under normal operations, electrical current (I) flows from the transformer 110 via the phase / live conductor 120, through the EV charging load 160, and back to the transformer 110 via the PEN conductor 130. In the event of an electrical fault in the EV charger, if a human comes into contact with the EV body / chassis 150, they should be safe. This is because any fault current should be carried back to the supply side via the PE conductor 170 and the PEN conductor 130, which is grounded at node 140. Therefore, the protective earth conductor 170 should ensure the safety of users in the event of an electrical fault, providing an important safety feature for EV charging infrastructure. Figure 2 illustrates a schematic diagram of the power supply system 100 for charging an Electric Vehicle (EV), but with an open circuit fault present. Like reference signs are used to denote like features vis-a-vis Figure 1. In the example of Figure 2, PEN conductor line 130 is broken, resulting in the transformer 110 being connected to earth connection 140 via line 130a, which is the remaining portion of old line 130 that is still in connection with the transformer 110. The remainder of old line 130 that is still in connection with EV charger 160 is now represented by line 130b. In the example of Figure 2, the power supply system 100 is dangerous due to the open circuit between lines 130a and 130b. Under operation, electrical current flows from the transformer 110, via the live / phase conductor 120, through the EV charging load 160, through the neutral conductor 180 and the PE conductor 170 to the EV body / chassis 150. It cannot return safely to the transformer 110, as it normally would, because of the open circuit break between lines 130a and 130b. Therefore, due to the open circuit fault, the EV charger chassis may become dangerous. In the event of a human 280 touching the EV charger chassis, the human 280 may experience an electric shock as they may complete the circuit between the EV body / chassis 150 and ground, resulting in the current I flowing through them to earth 290 / 140 and then back to the transformer 110. Therefore, it may be important to identify when such an open circuit fault occurs, so that the dangerous situation can be prevented. Such detection of faults is now requirement in the UK under the IET wiring regulation 722.411.4.1, as explained above. The present disclosure provides an effective mechanism for detecting such faults. By identifying open circuit faults in EV chargers, the solution disclosed herein can ensure that the EV charging infrastructure remains safe and reliable for users. Figure 3 is a circuit diagram 300 to help in understanding an example of the present disclosure. The circuit diagram 300 comprises a first phase supply with voltage VI, a second phase supply with voltage V2, and a third phase supply with voltage V3 all coupled to an EV load 310. The load of the EV that each phase of the three phase supply sees is represented by a first resistor RI, a second resistor R2 and a third resistor R3. The positive side of the first phase supply is connected to a first node LI (L is the phase conductor), and the first side of RI is also connected to LI. Similarly, the positive side of the second phase supply is connected to a second node L2, and the first side of R2 is also connected to L2. The positive side of the third phase supply is connected to a third node L3, and the first side of R3 is also connected to L3. The negative side of each phase supply is connected to the PEN conductor, which is earthed on the supply side. The second side of RI is connected to the neutral conductor N, the second side of R2 is connected to N, and the second side of R3 is connected to N. A protective earth conductor PE is connected to PEN on the customer side and, as explained earlier, will usually be coupled to the EV body / chassis. As will be well understood by the skilled person, in a three phase supply, each phase voltage is 120 degrees out of phase with respect to the other phases. Figure 4 illustrates the three-phase voltages across resistors RI, R2, and R3. The waveform of the voltage across RI is represented by waveform V(L1,N), which is the voltage between LI and N in circuit diagram 300. The waveform of the voltage across R2 is represented by waveform V(L2,N), which is the voltage between L2 and N in circuit diagram 300. The waveform of the voltage across R3 is represented by waveform V(L3,N), which is the voltage between L3 and N in circuit diagram 300. Figure 5 illustrates a circuit diagram 500 that shows an example of an open circuit fault, of the same type as explained earlier with reference to Figure 2. Like reference signs are used to denote like features vis-a-vis Figure 3. In the circuit diagram 500 of Figure 5, the neutral conductor N on the customer side is disconnected from earth, resulting in a potentially hazardous PEN fault. Detecting such faults may be important to prevent dangerous situations from occurring. The IET wiring regulation 722.411.4.1 requires that a PEN fault is detected in the event of the voltage between the circuit protective conductor (i.e., the neutral conductor N or the PE conductor) and earth exceeds 70 V rms due to an open-circuit fault in the PEN conductor. Figure 6 illustrates the three-phase voltages across resistors RI, R2, and R3 similar to Figure 4. However, as can be seen in Figure 6, compared with Figure 4 the voltages are no longer of the same amplitude and may optionally also have additional phase offsets (i.e., they may no longer be 120deg out of phase with each other) which may be as a result of load resistance on each phase. Figure 6 also illustrates the PEN fault voltage (V(PE,EAETH)), which is the voltage between the PE conductor (or neutral conductor N) and earth. However, it may be difficult to directly measure the PEN fault voltage (the voltage between the PE conductor or the neutral conductor and earth) because customer premises, particularly domestic customers, rarely have a reliable, truly earthed connection owing to the difficult and cost associated with installing a true earth point. Instead, they typically rely on the PEN arrangement of Figure 1, which means there is no true earth reference at the customer premises in the event of an open circuit PEN fault, as explained with reference to Figure 2. Therefore, traditional methods of measuring the PEN fault voltage tend to require the use of complex circuitry and additional hardware, such as the installation of an earthing rod at the customer premises, which may lead to additional complications and cost to the EV charging system. The present disclosure provides a less complex and cost-effective solution for detecting such faults. The solution disclosed herein provides an electronic device for detecting a Protective Earth and Neutral (PEN) fault in an Electric Vehicle (EV) charger supplied from a three phase power supply. The electronic device is configured to derive a reference voltage based on measured voltages between the three phase conductors and a reference conductor of the three phase power supply, and detect a PEN fault based on a comparison of the reference voltage with a threshold voltage. The neutral conductor, N, or the protective earth conductor, PE, maybe used as a reference conductor. The voltages between each of the three phase conductors and the reference conductor of the three phase power supply are often already measured in an EV charging system e.g., for metrology reasons. Therefore, leveraging these measurements means that often the disclosed PEN fault functionality may be implemented within existing hardware, without requiring additional hardware or costly installation / implementation. The inventors have realised that the reference voltage derived from the phase voltages is equivalent to the PEN fault voltage (the voltage between the neutral conductor and earth). Therefore, the IET wiring regulation 722.411.4.1 requirement of detecting a PEN fault in the event of the voltage between the circuit protective conductor (or the neutral conductor) and earth exceeding 70 V rms due to an open-circuit fault in the PEN conductor can be met by monitoring the reference voltage. In this example, to meet IET wiring regulation 722.411.4.1 requirement, the threshold voltage is 70 V rms. However, any alternative threshold voltage may be used. The electronic device disclosed herein derives the reference voltage from a first voltage VI, a second voltage V2 and a third voltage V3. VI is measured between a first phase conductor of the three phase power supply and a reference conductor associated with the three phase power supply (eg, the PE conductor or the neutral, N, conductor), V2 is measured between a second phase conductor of the three phase power supply and the reference conductor, and V3 is measured between a third phase conductor of the three phase power supply and the reference conductor. The reference voltage, Vref, may be found as follows: Vref = -(VI + V2 + V3) / 3 In this case, the reference voltage is the inverted average, in particular the inverted mean, of the three measured voltages. It is not necessary to invert the mean to calculate the reference voltage. In some examples, the reference voltage is the average, in particular the mean, of the three measured voltages, without inversion. In the UK regulations, a PEN fault is defined with respect to a threshold voltage that is an rms reference voltage (in particular, voltages excessing a threshold voltage of 70V rms). Therefore, in order to detect a PEN fault, the rms of Vref may be determined and then compared to the threshold voltage, such as 70V rms. If the rms of the reference voltage Vref exceeds the threshold, a PEN fault is detected. If it is less than the threshold, no PEN fault is detected. In some examples, the electronic device is also configured to detect an interruption to a phase conductor of the three phase power supply based on a comparison of at least one of the first voltage, the second voltage, the third voltage or phase to phase voltages of the phase conductors with a second threshold. Although, the first voltage, the second voltage and the third voltage can be used to detect interruption to a phase conductor, the use of the phase to phase voltages of the phase conductors to detect an interruption to a phase conductor may be a more reliable way of detecting phase conductor interruption. The second threshold may be set based on a percentage drop of the supply voltage in the respective phase conductor or the phase to phase voltages of the phase conductors. For example, if under normal operations, the supply voltage for a phase conductor is 400V rms phase to phase, an interruption may be defined by a predetermined percentage drop in the supply voltage for the phase conductor e.g., 20%. In this example where the normal voltage is 400V rms, a drop of 20% would reduce the voltage to 320V rms. Therefore, in this example the second threshold may be 320V rms and if the phase to phase rms voltage is less than the second threshold it may be assumed that the phase conductor is interrupted. Optionally, in the event that an interruption to a phase supply is detected, the electrical supply (e.g., all three phases) may be disconnected. Figure 7 is a block diagram showing a system 700 for detecting PEN faults according to an example. The system 700 comprises an EV 710, which is connected to supply lines LI, L2, and L3 of a three-phase power supply for charging the EV 710. Additionally, the EV 710 is connected to a neutral conductor N and a protective earth conductor PE, which are associated with the three-phase power supply. System 700 comprises a measurement unit 720 which is configured to measure the phase voltage of each supply line LI, L2 and L3 relative to a reference conductor, and output the phase voltage measurements VI, V2, V3 to an electronic device 730, which may also be referred to as a fault detector 730. In this example, the reference conductor is the neutral conductor N, but the measurement unit 720 may additionally or alternatively be coupled to the PE conductor, in which case the reference conductor may be the PE conductor. The measurement unit 720 is configured to measure a first voltage Vi by measuring the voltage between LI and the reference conductor. The measurement unit 720 is configured to measure a second voltage V2 by measuring the voltage between L2 and the reference conductor. The measurement unit 720 is configured to measure a third voltage V3 by measuring the voltage between L3 and the reference conductor. The fault detector 730 is configured to detect a PEN fault based on the three voltage measurements Vi, V2 and V3, as explained earlier. Upon detection of a PEN fault, the fault detector 730 may perform at least one of the following: generate and output a fault flag 740 indicative of the detection of the PEN fault, generate and output an alarm trigger 750 to trigger an alarm and / or generate and output a power supply disable signal 760 to disable the three phase power supply to the EV charger (for example, using relay switches in the EV charger apparatus that are configured to open on receipt of a power supply disable signal 760, thereby isolating the EV from the power supply). The output(s) of the fault detector 730 may be coupled to any suitable apparatus / device that is configured act on the signal, such as a relay switch controller, or an audio / visual alarm system, or a fault recording / diagnostics module, etc. In some examples, the fault detector 730 is configured to detect an interruption to a phase conductor of the three phase power supply (as explained earlier) and upon detection of the interruption, the fault detector 730 may perform at least one of the following: generate and output an interruption flag indicative of the detection of the interruption, generate and output an interruption alarm trigger to trigger an alarm, and / or generate and output the power supply disable signal 760 to disable the three phase power supply to the EV charger. In this example, the fault detector 730 receives voltage measurements from the measurement unit 720. However, in other examples, the measurement unit 720 may be integrated into the fault detector 730 such that the fault detector 730 is able to perform its own voltage measurements. In some example, the measurement unit 720 may be configured to measure the voltages digitally using analog-to-digital converters (ADCs) and supply the voltage measurements VI, V2 and V3 as digital values. Optionally, the measurement unit 720 may also be configured to measure the phase current supplied via one or more of the phase conductors LI, L2, L3, for example using a shunt resistor, or a current transformer (CT), at each phase conductor, coupled to a suitable measurement device such as an ADC. Figure 8 is a block diagram showing a system 800 for detecting PEN faults according to another example. Like reference signs are used to denote like features vis-a-vis Figure 7. The difference between system 800 and system 700 is that the protective earth conductor is used as a reference conductor for making the voltage measurements instead of the neutral conductor. The protective earth conductor and the neutral conductor are typically connected together at the customer side and therefore typically are at the same potential. Figure 9 is a block diagram showing a system 800 for detecting PEN faults according to another example. Like reference signs are used to denote like features vis-a-vis Figure 7. In addition to the component of systems 700 and 800, system 900 further comprises an analysis unit 910 and a customer MCU 920. The measurement unit 720 may be configured to use either of the neutral conductor or the protective earth conductor as reference conductor for measurement. The measurement unit 720 is configured to measure voltages Vi, V2 and V3, and additionally currents h, h and h supplied by the three phase conductors LI, L2 and L3 respectively. An analysis unit 910 receives the voltage and current measurements. The analysis unit 910 comprises the fault detector 730 (for example, it is configured to perform the PEN fault detection functionality described above, and optionally also the interruption detection functionality). The analysis unit 910 may be configured to perform various different EV charging functions using at least some of the measurements Vi, V2 and V3 and h, I2 and I3. For example, it may perform metrology functions such as measuring active and apparent power, active energy, perform rms calculations, detecting over / under current / voltage conditions, waveform streaming etc. At least some of the results of the operations performed by the analysis unit 901 may be transmitted to a customer's MCU 920 for example, such as via a SPI interface. The results of the fault detector 730 operations, for example the fault flag 740, alarm trigger 750 and / or power supply disable signal 760, may also be output to the customer's MCU 920, which may then act appropriately (for example, acting to isolate the EV charger, and therefore the EV, from the power supply). As a result, it can be readily seen that the PEN fault detection functions disclosed herein may be straightforwardly implemented within existing hardware, such as the analysis unit 910, using measurements that are already used by that existing hardware for other purposes. The PEN fault detection functionality disclosed herein may be implemented in hardware, for example via logic, and / or in software. For example, the fault detector 730 may be implemented using digital logic circuits, which may be fixed circuits or reconfigurable circuits such as FPGAs, or through the use of software code that cause the functions described above to be performed when the code is executed on one or more processors , or a combination thereof. The implementation may include the use of a combination of hardware and software elements to achieve the desired functionality. In one example, the analysis unit 910 may be a microprocessor that is configured to perform the PEN fault detection functions disclosed herein, as well as one or more additional functions such as metrology. Figure 10 is a block diagram showing a system 1000 for detecting PEN faults according to another example implementation. Like reference signs are used to denote like features vis-a-vis Figure 9. System 1000 comprises an EV charger 1010. The EV charger 1010 comprises the measurement unit 720, the analysis unit 910, the customer MCU 920 and additionally a relay arrangement 1020. The relay arrangement 1020 is configured to disconnect the supply line (LI, L2, L3, N, and PE conductors) from the EV 710 upon detection of a fault. By disconnecting the supply lines upon detection of a fault, the system 1000 can prevent dangerous situations from occurring and allow for the safe charging of EV 710. In this case, the relay arrangement 1020 contacts position is controlled by the customer MCU 920, which receives a signal from the fault detector 730 upon detection of a fault. Alternatively, the fault detector 730 could directly control the operation of the relay arrangement 1020, or the analysis unit 910 could be configured to control the relay arrangement 1020 upon detection of a fault. The above embodiments are to be understood as illustrative examples. Further embodiments are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims. For example, Figures 7 to 10 show the measurement unit 720 being coupled to the neutral conductor, N, and measuring each phase voltage LI to L3 relative to N. The measurement unit 720 may additionally or alternatively be coupled to the PE conductor and measure each phase voltage LI to L3 relative to PE conductor such that the measurements VI to V3 output to the analysis unit are measurements relative to the PE conductor (which should be at the same potential as the neutral conductor, N). The above explanation focusses on EV chargers being configured to detect a PEN fault. However, in an alternative, the fault detector 730 may be implemented anywhere, or integrated into any device or system. For example, it may form part of a utility meter and be configured to detect a PEN fault in the premises within which the utility meter is installed, regardless of whether or not the premises includes an EV charger. Whilst detection of PEN faults is a requirement of EV charging regulations, there may still be benefits in detecting PEN faults in electrical installations even if they do not have an EV charger, and then optionally taking appropriate action when one is detected, such as disconnecting the supply to the premises and / or alerting the owner of the premises, etc. Furthermore, the fault detector, or analysis unit, may be sold as a standalone chip / unit for fitting or retrofitting into a system / device, such as fitting or retrofitting into an EV charger or utility meter.

Claims

1. An electronic device for detecting a Protective Earth and Neutral, PEN, fault in a three phase power supply, the electronic device being configured to:5 determine a reference voltage derived from a first voltage, a second voltage and athird voltage each associated with a respective phase of the three phase power supply, wherein the first voltage is measured between a first phase conductor of the three phase power supply and a reference conductor associated with the three phase power supply, wherein the second voltage is measured between a second phase conductor of the three10 phase power supply and the reference conductor, and wherein the third voltage is measured between a third phase conductor of the three phase power supply and the reference conductor; anddetect a PEN fault based on a comparison of the reference voltage with a threshold voltage.

152. The electronic device of claim 1, wherein the reference conductor is a neutral conductor associated with the three phase power supply or a protective earth conductor associated with the three phase power supply.

3. The electronic device of either of claims 1 or 2, wherein determining the reference voltage comprises determining an average of the first voltage, the second voltage and the third voltage.

4. The electronic device of any preceding claim, wherein the comparison of the 25 reference voltage with the threshold voltage comprises deriving a root mean square, rms, reference voltage from the reference voltage.

5. The electronic device of claim 4, wherein detecting the PEN fault comprises determining that the rms reference voltage exceeds the threshold voltage.

306. The electronic device of any preceding claim, wherein the threshold voltage is 70 volts rms.

7. The electronic device of any preceding claim, wherein the electronic device is 35 further configured to detect an interruption to at least one phase conductor of the three phase power supply based on a comparison against a second threshold of at least one of the following:the first voltage;the second voltage;the third voltage;a voltage difference between the first phase conductor and the second phase5 conductor;a voltage difference between the second phase conductor and the third phase conductor; and / ora voltage difference between the third phase conductor and the first phase conductor.

108. The electronic device of claim 7, wherein the comparison of at least one of the first voltage, the second voltage, the third voltage, the voltage difference between the first phase conductor and the second phase conductor, the voltage difference between the second phase conductor and the third phase conductor and / or the voltage difference 15 between the third phase conductor and the first phase conductor with the second thresholdcomprises:deriving at least one of a root mean square, rms, first voltage from the first voltage, an rms second voltage from the second voltage, an rms third voltage from the third voltage, an rms fourth voltage from the voltage difference between the first phase conductor and the second phase conductor, an rms fifth voltage from the voltage difference between the second phase conductor and the third phase conductor and / or an rms sixth voltage from the voltage difference between the third phase conductor and the first phase conductor; andcomparing the derived rms first voltage, rms second voltage, rms third voltage,25 rms fourth voltage, rms fifth voltage and / or rms sixth voltage with the second threshold.

9. The electronic device of claim 8, wherein detecting the interruption to the at least one phase conductor of the three phase power supply comprises determining that the rms first voltage, the rms second voltage, the rms third voltage, the rms fourth voltage, the 30 rms fifth voltage and / or the rms sixth voltage is less than the second threshold voltage.

10. The electronic device of any of claims 7 to 9, wherein the second threshold voltage is derived from the nominal voltage of the three phase power supply.35 11. The electronic device of any preceding claim, wherein the electronic device isfurther configured to measure the first voltage, the second voltage and the third voltage.

12. The electronic device of any preceding claim, wherein the electronic device is further configured to, upon detection of the PEN fault, generate a flag indicative of the detection of the PEN fault.

13. The electronic device of any preceding claim, wherein the electronic device is further configured to, upon detection of the PEN fault, trigger an alarm.

14. The electronic device of any preceding claim, wherein the electronic device is further configured to, upon detection of the PEN fault, disable the three phase power supply to an EV charger.

15. A system for use in an Electric Vehicle, EV, charger, the system comprising:the electronic device of any preceding claim; anda metrology measurement unit configured to measure the first voltage, the second voltage and the third voltage; andoutput, to the electronic device, measurements of the first voltage, second voltage and third voltage.

16. An Electrical Vehicle, EV, charger comprising the system of claim 15.

17. A method for detecting a Protective Earth and Neutral, PEN, fault in a three phase power supply, the method comprising:determining a reference voltage derived from a first voltage, a second voltage and a third voltage each associated with a respective phase of the three phase power supply, wherein the first voltage is measured between a first phase conductor of the three phase power supply and a reference conductor associated with the three phase power supply, wherein the second voltage is measured between a second phase conductor of the three phase power supply and the reference conductor, and wherein the third voltage is measured between a third phase conductor of the three phase power supply and the reference conductor; anddetecting a PEN fault based on a comparison of the reference voltage with a threshold voltage.

18. The method of claim 17, wherein the reference conductor is a neutral conductor associated with the three phase power supply or a protective earth conductor associated with the three phase power supply.

19. The method of either of claims 17 or 18, wherein determining the reference voltage comprises determining an average of the first voltage, the second voltage and the third voltage.5 20. The method of any of claims 17 to 19, wherein the comparison of the referencevoltage with the threshold voltage further comprises deriving a root mean square, rms, reference voltage from the reference voltage.

21. The method of claim 20, wherein detecting the PEN fault comprises determining 10 that the rms reference voltage exceeds the threshold voltage.

22. The method of any of claims 17 to 21, wherein the threshold voltage is 70 volts rms.15 23. The method of any of claims 17 to 22, wherein the method further comprisesdetecting an interruption to at least one phase conductor of the three phase power supply , based on a comparison against a second threshold of at least one of the following:the first voltage;the second voltage;<n20the third voltage;a voltage difference between the first phase conductor and the second phase CO conductor;a voltage difference between the second phase conductor and the third phase conductor; and / or25 a voltage difference between the third phase conductor and the first phaseconductor.

24. A computer program comprising instructions which, when executed by at least one processor, perform the method of any of claims 18 to 23.

25. A computer readable medium comprising the computer program of claim 24.

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